1. Database Systems: Design, Implementation, and Management Ninth Edition
Chapter 4
The Relational Model Charactristics

2. Objectives In this chapter, students will learn:
That the relational database model offers a logical view of data
About the relational model’s basic component: relations
That relations are logical constructs composed of rows (tuples) and columns (attributes)
That relations are implemented as tables in a relational DBMS
Database Systems, 9th Edition

3. Objectives (cont’d.)
About relational database operators, the data dictionary, and the system catalog
How data redundancy is handled in the relational database model
Why indexing is important
Database Systems, 9th Edition

4. A Logical View of Data Relational model Table
View data logically rather than physically
Table
Structural and data independence
Resembles a file conceptually
Relational database model is easier to understand than hierarchical and network models
Database Systems, 9th Edition

5. Tables and Their Characteristics
Logical view of relational database is based on relation
Relation thought of as a table
Table: two-dimensional structure composed of rows and columns
Persistent representation of logical relation
Contains group of related entity occurrences (entity set)
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8. Keys Each row in a table must be uniquely identifiable
Key is one or more attributes that determine other attributes
Key’s role is based on determination
If you know the value of attribute A, you can determine the value of attribute B
Functional dependence
Attribute B is functionally dependent on A if each value in column A determines one and only one value in column B
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10. Keys (cont’d.) Composite key Key attribute Candidate key
Any determinant Composed of more than one attribute
Key attribute
Any attribute that is part of a key
Candidate key
Any determinant that determines ALL other attributes in the relation ( table )
Database Systems, 9th Edition

11. Keys (cont’d.)
Nulls
No data entry at all .It does not mean zero or space
Not permitted in primary key to maintain entity integrity
Should be avoided in other attributes
If they are used improperly they Can represent:
An unknown attribute value
A known, but missing, attribute value
A “not applicable” condition
Database Systems, 9th Edition

12. Keys (cont’d.) Nulls (cont’d.)
Can create problems when functions such as COUNT, AVERAGE, and SUM are used
Can create logical problems when relational tables are linked
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13. Keys (cont’d.)
Controlled redundancy makes the relational database work
Tables within the database share common attributes that enables them to be linked together
Multiple occurrences of values not redundant when required to make the relationship work
Redundancy exists only when there is unnecessary duplication of attribute values
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15. Keys (cont’d.) Foreign key (FK) Secondary key
An attribute whose values match primary key values in the related table
Secondary key
Key used strictly for data retrieval purposes
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17. Integrity Rules
Many RDBMs enforce integrity rules automatically but t is much safer to ensure that application design conforms to integrity rules
We have 2 integrity rules :
Entity integrity :
ALL primary key values must be unique and does not contain null values
2) Referential integrity:
FK values should refer to an existing valid tuple ( raw ) in another relation ( table )
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20. Designers use flags to avoid nulls Flags indicate absence of some value
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21. Relational Set Operators
Relational algebra
Defines theoretical way of manipulating table contents using relational operators
Closure :the use of relational algebra operators on existing relations produces new relations:
SELECT
DIFFERENCE
PROJECT
JOIN
UNION
PRODUCT
INTERSECT
DIVIDE
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25. Give an example of using UNION /INTERSECT/ DIFFERENCE
Database Systems, 9th Edition

26. Relational Set Operators (cont’d.)
Natural Join
Links tables by selecting rows with common values in common attribute(s)
Equijoin
Links tables on the basis of an equality condition that compares specified columns
Theta join
Any other comparison operator is used
Outer join
Matched pairs are retained, and any unmatched values in other table are left null
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31. Who is using Room # 410 and 411 together this semester?
TEACHER
411
Malak
Anwar
410
Amal
Masheal
ROOM #
410
411
TEACHER
Malak
Database Systems, 9th Edition

32. The Data Dictionary and System Catalog
Provides detailed description of all tables found within the user/designer-created database
Contains (at least) all the attribute names and characteristics for each table in the system
Contains metadata: data about data
System catalog
Contains metadata
Detailed system data dictionary that describes all objects within the database
Is a system-created database whose tables store the user/designer-created database characteristics and contents. therefore, the system catalog tables can be queried just like any user/designer-created table
Automatically produces database documentation which allows the RDBMS to check for and eliminate homonyms & synonyms

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34. Relationships within the Relational Database
1:M relationship
Relational modeling ideal
Should be the norm in any relational database design
1:1 relationship
Should be rare in any relational database design
Database Systems, 9th Edition

35. Relationships within the Relational Database (cont’d.)
M:N relationships
Cannot be implemented as such in the relational model
M:N relationships can be changed into two1:M relationships
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36. The 1:M Relationship Relational database norm
Found in any database environment
Database Systems, 9th Edition

37. Another EX: page 77 / 123
Each course can generate many classes
Each class refers to only one course
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38. The 1:1 Relationship
One entity related to only one other entity, and vice versa
Sometimes means that entity components were not defined properly
Could indicate that two entities actually belong in the same table
Certain conditions absolutely require their use
Database Systems, 9th Edition

39. Optional
Look at the figure 3.23 /Page 79 /125
Another relationship: department employs professor
Database Systems, 9th Edition

40. The M:N Relationship
M:N relationship is not supported directly in the relational model
Can be implemented by creating a new entity (composite entity/bridge entity/associative entity) ---linking table witch include the primary keys of the tables that are to be linked
Database Systems, 9th Edition

41. Look at figure 3.2 page 81
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42. Or you can create new primary key as ENROLL_LINE
What is the appropriate data type for this key?
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46. Data Redundancy Revisited
Data redundancy leads to data anomalies
Can destroy the effectiveness of the database
Foreign keys
Control data redundancies by using common attributes shared by tables
minimize data redundancies
Sometimes, data redundancy is necessary
Look at figure 3.30 /page 85
Database Systems, 9th Edition

47. Information requirements
Design elegance
Processing speed
Database Systems, 9th Edition

48. Indexes Orderly arrangement to logically access rows in a table
Is composed of an index key & set of pointers
Index key
Index’s reference point
Points to data location identified by the key
Unique index
Index in which the index key can have only one pointer value (row) associated with it
A table can have many indexes, but each index is associated with only one table
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50. Codd’s Relational Database Rules
In 1985, Codd published a list of 12 rules to define a relational database system
Products marketed as “relational” that did not meet minimum relational standards
Even dominant database vendors do not fully support all 12 rules
Database Systems, 9th Edition

51. Summary Tables are basic building blocks of a relational database
Keys are central to the use of relational tables
Keys define functional dependencies
Superkey
Candidate key
Primary key
Secondary key
Foreign key
Database Systems, 9th Edition

52. Summary (cont’d.)
Each table row must have a primary key that uniquely identifies all attributes
Tables are linked by common attributes
The relational model supports relational algebra functions
SELECT, PROJECT, JOIN, INTERSECT UNION, DIFFERENCE, PRODUCT, DIVIDE
Good design begins by identifying entities, attributes, and relationships
1:1, 1:M, M:N
Database Systems, 9th Edition

53. Q8 ,9,10 Natural JOIN Database Systems, 9th Edition STU_CODE PROF_CODE
DEPT_CODE
128569 2 6
512272 4
531235
553427 1
STU_CODE
PROF_CODE
DEPT_CODE
128569 2 6
512272 4
531235
553427 1
Database Systems, 9th Edition

54. Q11,12,13,14 Database Systems, 9th Edition BOOTH_PRODUCT BOOTH_PRICE
Chips
1.5
Cola
1.25
Energy Drink 2
Chocolate Bar 1
BOOTH_PRODUCT
BOOTH_PRICE
Energy Drink 2
MACHINE_PRODUCT
MACHINE_PRICE
Chips
1.25
Chocolate Bar 1
Database Systems, 9th Edition